Petrochemistry, U-Pb (zircon) age, and palaeotectonic setting of the Lampang volcanic belt, northern Thailand

Two NE-trending belts of mainly subaerial dacitic to rhyolitic flows and tuffs occur in the area between the towns of Lampang and Denchai in northern Thailand. In the western belt (Doi Ton), the rocks have been pervasively altered to quartz keratophyre; rocks in the eastern belt (Doi Luang) are gene...

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Bibliographic Details
Published in:	Journal of the Geological Society Vol. 157; no. 3; pp. 553 - 563
Main Authors:	Barr, S. M, Macdonald, A. S, Dunning, G. R, Ounchanum, P, Yaowanoiyothin, W
Format:	Journal Article
Language:	English
Published:	London Geological Society of London 01-05-2000 The Geological Society of London Geological Society Geological Society Publishing House
Subjects:	absolute age Asia chemical composition Crystalline rocks dacites dates Denchai Thailand Doi Luang Thailand Doi Ton Thailand Earth sciences Earth, ocean, space Exact sciences and technology Far East geochemistry Geochronology Igneous and metamorphic rocks petrology, volcanic processes, magmas igneous rocks island arcs Isotope geochemistry. Geochronology Jinghong Thailand keratophyre Lampang Thailand Lincang Thailand Mae Man Group Mesozoic metals Middle Triassic migration of elements Minerals nesosilicates northern Thailand orthosilicates Phetchabun Thailand plate convergence pyroclastics quartz keratophyre rare earths rhyolites rock, sediment, soil silicates Sm/Nd suture zones tectonics Thailand Triassic tuff U/Pb volcanic belts volcanic rocks Volcanoes zircon zircon group Far East Thailand Lampang Thailand Triassic tectonics volcanic arc Thailand Lampang Mesozoic keratophyre dacites Sm/Nd orogenic magmatism rare earths accretion zircon Middle Triassic Terranes silicates lava flows dating nesosilicates volcanic rocks volcanic arcs igneous rocks rhyolites U/Pb chemical analysis quartz keratophyre pyroclastics Asia tuff tectonic setting alteration Phanerozoic plate convergence concordia diagram
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Summary:	Two NE-trending belts of mainly subaerial dacitic to rhyolitic flows and tuffs occur in the area between the towns of Lampang and Denchai in northern Thailand. In the western belt (Doi Ton), the rocks have been pervasively altered to quartz keratophyre; rocks in the eastern belt (Doi Luang) are generally less altered. Mobile chemical components such as Na2O and K2O show wide variation, particularly in samples from the Doi Ton belt. However, low Zr/TiO2 ratios and low Nb and Ta contents support an origin at a convergent plate margin. A positive epsilon Nd value of +4.9 for rhyolite from the Doi Luang belt supports derivation from a primitive crustal source. A rhyolite sample from the Doi Luang belt yielded a U-Pb zircon age of 240±1 Ma (early Mid-Triassic). The Doi Ton and Doi Luang belts are part of the Lampang volcanic belt, which can be traced to the north into the Lincang-Jinghong volcanic belt in southern China. Comparison with published petrological data from the Lincang-Jinghong belt shows strong similarity, including the widespread development of keratophyric mineralogy and chemistry. The Lampang-Lincang-Jinghong belt formed at an early Mid-Triassic convergent plate margin, and is similar in age and tectonic setting to the more mafic Phetchabun volcanic belt on the east side of the Nan River suture zone. These data constrain the timing of final amalgamation between the Indochina and Shan-Thai terranes to Mid-Triassic or younger.
ISSN:	0016-7649 2041-479X
DOI:	10.1144/jgs.157.3.553